Radio telephone system control method

ABSTRACT

In a method and apparatus for controlling a radio telephone system, a speech channel is established between the slave radio set of a plurality of radio telephone sets and a radio set of a base unit. An intercom switch for selecting intercom performances is provided for respective radio telephone sets. The slave radio sets of the radio telephone sets are turned OFF when the intercom switch is OFF, and transmitters of the slave radio sets of the radio telephone sets are turned ON. Consequently the connection between a wired telephone channel and the plurality of radio telephone sets can be controlled with a single base unit connected to the wired telephone channel.

This is a division of application Ser. No. 178,844, filed Apr. 7, 1988,now U.S. Pat. No. 4,897,864 which is a continuation of application Ser.No. 900,620, filed Aug. 26, 1986 now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a radio telephone system control apparatus anda method for controlling the connection of a base unit connected to awired telephone channel and a plurality of radio telephone handsetsconnected to the base unit through radio channels, and more particularlyan apparatus for controlling an intercom connection among a plurality ofthe radio telephone handsets.

2. Description of the Related Arts

Radio telephone systems comprise a base unit connected to wiredtelephone lines and one or more radio telephone handsets connected tothe base unit through radio channels, such as a cordless telephone. Thecordless telephone apparatus consists of a base unit connectingapparatus connected to wired telephone channels, and a radio telephonehandset provided for the base unit in a one to one correspondence, andthe frequencies of its signals are fixed such that up radio channelsfrom the radio telephone handsets to the base unit utilize signals offrequency f₁, while down telephone channels from the base unit to theradio telephone handsets utilize signals of frequency f₂. As aconsequence, where two radio telephone handsets are utilized, it isnecessary to install two base units.

With such a radio telephone system utilizing two radio telephonehandsets and two base units, however, two radio telephone handsets arenot usually used simultaneously, so that provision of two base units isnot economical.

In recent years, for the purpose of efficiently utilizing allocatedfrequencies, a so-called multi-channel access system has been adoptedwherein a frequency being used is determined by utilizing a commonchannel, for example, a control channel between a plurality of baseunits, and then the channel is switched to a speech channelcorresponding to the frequency. However, when such a multi-channelaccess system is adopted, there is a problem in the case where a baseunit is provided for each of the two radio telephone handsets that whena ring signal is received from a wired telephone handset, the two baseunits start connection control using respective control channelssimultaneously, whereby radio waves from these control channelsinterfere with each other. Thus, the connection control is sometimesmade impossible.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide a radio telephonesystem control apparatus and a method which enables connection controlfor a plurality of radio telephone handsets with a single base unit aswell as to provide an intercom function.

According to one aspect of this invention, there is provided a radiotelephone system control apparatus comprising a plurality of radiotelephone handsets, each having a handset transceiver; a base unitconnected to a wired telephone channel for exchanging signals betweensaid base unit and the handset transceiver of said radio telephonehandsets; means for establishing a speech channel between the saidplurality of radio telephone handsets and a base unit transceiverintercom switch means provided for respective radio telephone handsetsfor selecting an intercom performance; means for turning OFF atransmitter of a radio telephone handset provided with said intercomswitch means when said intercom switch means is OFF; and means forturning ON a transmitter of a radio telephone handset provided with saidintercom switch means when the same is turned ON.

According to a modified embodiment of this invention, there is provideda method of controlling a radio telephone system of the type whereinconnections between a wired telephone channel and a plurality of radiotelephone handsets are controlled by a single base unit connected tosaid wired telephone channel, said method comprising the steps of:establishing a speech channel between said plurality of radio telephonehandsets and a base unit; providing an intercom switch for respectiveradio telephone handsets to select intercom performances; turning OFF ofa transmitter of said radio telephone handsets when the intercom switchis OFF, and turning ON the transmitter of the radio telephone sets whensaid intercom switch is ON.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a block diagram showing the detail of one embodiment of thisinvention;

FIGS. 2 through 6 show flow charts showing the operation of theembodiment shown in FIG. 1;

DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the radio telephone system according to thisinvention shown in FIG. 1 comprises one base unit 4 and two radiotelephone handsets 5 and 5'. For the purpose of simplifying thedescription, only two radio telephone sets are shown but it will beclear that the invention is also applicable to three or more radiotelephone handsets. The base unit 4 is connected to a wired telephoneline, not shown, through a terminal 3. A signal from the wired telephoneline inputted to terminal 3 is supplied to a transmitter 16 via a linerelay 23 and a hybrid circuit 22, while the output from the transmitter16 is sent out from an antenna 12 via an antenna duplexer 13. On theother hand, a signal received by antenna 12 is applied to a receiver 14through antenna duplexer 13, and the output from the receiver 14 issupplied to the wired telephone channel via hybrid circuit 22, linerelay 23 and terminal 3. A synthesizer 21 is provided for determiningthe radio frequency of the transmitter 16 and the receiver 14, and acontrol unit 15 is provided for the purpose of controlling transmitter16, receiver 14 and synthesizer 21. Read only memory devices (ROM) 18and 18' are provided for the purpose of storing identificationinformation for controlling the connections to radio telephone handsetsto be described later, the Identification information being used in thecontrol unit 15.

The radio telephone handsets 5 and 5' are connected to the base unitthrough radio channels. The radio telephone handsets 5 and 5' have thesame construction except that their ROMs 17 and 17' store differentinformation. More particularly, element 6 bounded by dotted lines inFIG. 1 has the same construction for both telephone sets 5 and 5' sothat in the following description, elements utilized in radio telephonehandset 5' are designated by the same reference numerals as those usedin the radio telephone handset 5 except addition of a prime. The signaltransmitted from the base unit is received by an antenna 11 and appliedto a receiver 19 through an antenna duplexer 10, and the output of thereceiver 19 is supplied to a loudspeaker 29 to be connected to generatesound. A signal inputted to a microphone 30 is sent to the base unit 4via transmitter 8, antenna duplexer 10, and antenna 11. A synthesizer 20is provided for determining the radio frequency of receiver 19 andtransmitter 8, while a control unit 9 is provided for controllingreceiver 19, transmitter 8 and synthesizer 20. A loudspeaker 31connected to the synthesizer produces a call tone. A hook switch 7 isprovided to originate a call and to respond to the call tone produced bythe loudspeaker 31.

The information stored in ROMs 17 and 17' corresponds to that stored inROMs 18 and 18' of the base unit 4.

This embodiment employs a multichannel access system comprising a singlecontrol channel (C-CH) and a plurality, for example 45, of speechchannels. Thus a speech channel is established by commonly utilizing asingle control channel by a plurality of apparatus. The operation ofthis embodiment will be described with reference to the flow chartsshown in FIGS. 2 through 6.

FIG. 2 shows a flow chart for the case when an origination is issuedfrom radio telephone handset 5. At step 201, when the hook switch 7 ofthe radio telephone handset 5 is taken off hook at step 202, this statechange is detected by control unit 9 and this unit 9 turns ON thetransmitter 8, and then at step 203 the originating signal is sent tothe base unit 4 via antenna duplexer 10 and antenna 11. The transmissionof the originating signal from the radio telephone handset 5 to the baseunit 4 is made by using the control channel (C-CH). Upon termination ofthe transmission of the originating signal, at step 204, the controlunit 9 turns off the transmitter 8. At step 205, the base unit 4receives with receiver 14 the originating signal via antenna 12 andantenna duplexer 13 and the demodulated output from the receiver 14 isapplied to the control unit 15. Then at step 206, the control unit 15turns ON transmitter 16 for transmitting a call signal to radiotelephone handset 5' at step 207. The transmission of the call signalfrom the base unit 4 to the radio telephone handset 5' is performed byusing the control channel (C-CH). For the purpose of selectively sendingthe call signal to the radio telephone handset 5', identifyinginformation is incorporated into the call signal stored in the ROM 18'.When the radio telephone handset 5' receives the call signal, itcompares the identifying signal contained in the call signal with theinformation stored in ROM 17', and when they coincide with each other,the radio telephone handset 5' accepts the call signal. In thefollowing, a digit `2` shows a signal containing the identifying signalstored in ROM 18', while a digit `1` shows a signal containing anidentifying signal stored in ROM 18. An identifying signal stored inROMs 18, 18', 17 and 17' is made up of an identifying code common toboth radio telephone handsets 5 and 5' and individual identifying codesassigned to respective radio telephone handsets 5 and 5'. The commonidentifying code is used to identify the other radio telephone handset.

At step 208, the radio telephone handset 5' receives a call signal 2transmitted from the base unit 4 by receiver 19' through antenna 11' andantenna duplexer 10'. The demodulated output from receiver 19' issupplied to control unit 9' whereby it turns ON transmitter 8' at step209, and a call response signal 2 is sent to the base unit 4 at step210. As has been pointed out before, the call response signal 2 containsan identifying signal stored in ROM 17'. Upon termination of the callresponse signal 2, at step 211, the control unit 9' of the radiotelephone system 5' turns OFF transmitter 8'.

After sending the call signal 2 at step 207, at step 212 the base unit 4executes a judgement as to whether a predetermined time has elapsed ornot. When the result of the judgement shows that the predetermined timehas not yet elapsed, that is not time out, the program is transferred tostep 213 at which a judgement is made as to whether receiver 14 hasreceived a call response signal 2 from radio telephone handset 5' ornot. When the result of judgement at step 213 is NO, the program isreturned to step 312. When result of judgement at step 212 shows a timeout and when the result of judgement at step 213 shows receipt of a callresponse signal 2, the program is transferred to step 214. Moreparticularly, when a predetermined time has elapsed after sending out acall signal 2 from the base unit 4, or when a call response signal 2 isreceived from radio telephone handset 5', the program is transferred tostep 214.

At step 214, a channel designating signal 1 for designating apredetermined channel is transmitted to radio telephone handset 5 byusing the control channel. At step 215, the radio telephone handset 5executes a judgement as to whether the radio telephone handset 5 hasreceived the channel designating signal 1 or not. When the result ofjudgement is YES, the control unit 9 controls the synthesizer 20 forswitching the radio frequency of transmitter 8 and receiver 19 to thatcorresponding to a predetermined speech channel (S-CH₁) at step 216.After that, at step 217 a timer is operated and after a predeterminedtime, the transmitter 8 is turned ON at step 218.

Following the transmission of the channel designating signal at step214, at step 219, the base unit 4 sends out a channel designating signal2 to radio telephone handset 5' by using the control channel. Thechannel designating signal 2 designates the same speech channel as thechannel designating signal 1. Upon completion of the transmission of thechannel designating signal, at step 220, the base unit 4 turns OFFtransmitter 16 so as to control the synthesizer 21, thereby switchingthe transmission/reception frequency to that corresponding to speechchannel (S-CH₁) and then turning ON transmitter 16 at step 222. As aconsequence, speech between the base unit and the radio telephonehandset 5 becomes possible by utilizing the speech channel (S-CH₁).

At step 223, in radio telephone handset 5' a judgement is made as towhether the channel designating signal 2 sent from the base unit 4 hasbeen received or not. When the result of judgement executed at step 223is YES, the program is advanced to step 224 at which thetransmission/reception frequency is switched to that corresponding tospeech channel (S-CH₁) and at step 235, the state is changed to awaiting state. Under this state since the transmitter 8' at the radiotelephone handset 5' is OFF, the radio telephone handset 5' can receiveonly a signal from the base unit 4 utilizing speech channel (S-CH₁).

After turning ON the receiver 8 at step 218, the radio telephone handset5 turns ON the audio frequency circuit of the transmitter 8 and receiver19 at step 226. At step 222, the base unit turns ON transmitter 16 andthe turns ON line relay 23 at step 227 for closing a relay contact,whereby radio telephone handset 5 can establish voice communicationthrough a wired telephone line connected to terminal 3 of the base unit4 by using a handset speaker 29 and microphone 30. In this state, whenthe hook switch 7' of the radio telephone handset 5' now in the waitingstate is hooked OFF, the reception of speech is possible buttransmission thereof is impossible.

The operation of a case wherein a ring signal is received by to the baseunit from the wired telephone line will be described as follows.

FIG. 3 shows a flow chart showing the operation of a case in which aring signal is received by the base unit from a wired telephone line.The detection of the ring signal is made by judging the presence orabsence of the ring signal by the control unit 15 based on the outputsignal of a detecting circuit, not shown, connected to the wiredtelephone line. At step 301, when a ring signal is received by the baseunit, in other words, when the same is called by the wired telephoneline, at step 302 the base unit turns ON the transmitter 16 so as tosend out a paging signal containing a designating signal that designatesa predetermined speech channel at step 303. The paging signals are sentto respective radio telephone handsets in a predetermined order ofpriority which is determined by the order of inserting IC sockets intoROMs 18 and 18' or by the order of information prestored in ROMs 18 and18'. The order of priority may be set by an independent switch or thelike, or may be randomly set by generating a suitable random number.Further, the order of priority can be set according to the hysteresis ofthe connection to the wired telephone line. Thus, for example, the mostrecently used radio telephone handset or a radio telephone handset mostfrequently used can be set to the upper most order.

In the flow chart shown in FIG. 3, the radio telephone handset 5 is ahigher order of priority than the radio telephone handset 5'. Thus, atstep 303, a paging signal 1 is sent to radio telephone handset 5. Atstep 304, when the radio telephone handset 5 receives the paging signal1, transmitter 8 is turned ON at step 305, and a paging response signal1 is sent to the base unit at step 306.

The base unit 4 monitors the paging response signal 1. When the pagingsignal is received within a predetermined interval after sending out thepaging signal 1 at step 303, more particularly, at step 307, when it isjudged that there is no time out, and at step 308, when it is judgedthat the paging response signal 1 has been received, the program istransferred to step 309 for turning OFF receiver 16. Then at step 310, aradio channel is switched to a speech channel (S-CH₂). After that atstep 311, the transmitter 16 is turned ON.

At step 306, upon termination of the transmission of the paging responsesignal 1, at step 312, the radio telephone handset 5 turns OFFtransmitter 8 to switch the radio channel to the speech channel (S-CH₂).After that, at step 314, transmitter 8 is turned ON again, therebyestablishing a speech channel between base unit and radio telephone 5 byutilizing the speech channel (S-CH₂).

At step 311, the base unit turns ON transmitter 16 and then at step 315,the base unit sends out a bell ringing signal by using the speechchannel (S-CH₂). At step 319 as the radio telephone handset 5 receivesthe bell ringing signal, at step 320, a call tone is produced fromloudspeaker 31. At step 318 when the hook switch 7 is taken off hook inresponse to the call tone, at step 321, an off-hook signal is sent tothe base unit 4 through the speech channel (S-CH₂). Then at step 322,the audio frequency circuit is turned ON.

At step 316 when the base unit receives the off-hook signal from theradio telephone handset, at step 317, the line relay 23 is turned ON,whereby the radio telephone handset 5 can exchange speech with a wiredtelephone line through the base unit 4.

At step 307, when time out is judged, that is where a paging responsesignal 1 is not returned from the radio telephone handset after elapseof a predetermined interval, after sending out of the paging signal, atstep 323 a paging signal 2 for the radio telephone handset at the nextorder of priority is sent out. At step 324, when the radio telephonehandset 5' receives the paging signal 2, at step 325, the transmitter 8'is turned ON to send out the paging response signal 2 at step 326. Whenthis paging response signal 2 is received by the base unit 4 within apredetermined interval after sending out the paging signal 2, theprogram is transferred to step 309 at which the transmitter 16 is turnedOFF, and then the channel is switched to a speech channel (S-CH₂),whereby the transmitter 16 is turned ON again to send out a bell ringingsignal at step 315.

After sending out the paging response signal 2, the radio telephonehandset 5' causes the radio telephone handset 5 to execute theoperations, that is, a portion 24 of the flow chart bounded by dottedlines. More particularly, transmitter 8' is turned OFF first forswitching the speech channel (S-CH₂) and turning ON again thetransmitter 8'. When a bell ringing signal is received from the baseunit, a call tone is sent out. When the hook switch 7' is opened inresponse to the call tone, an off-hook signal is sent out and then theaudio frequency circuit is turned ON.

At step 316, when the base unit receives an off-hook signal from radiotelephone handset 5', at step 317, the line relay 23 is turned ON so asto connect the radio telephone handset 5' to the wired telephone linevia the base unit 4.

At step 307, when time out is judged, that is where a paging responsesignal 1 is not returned from the radio telephone handset after apredetermined time interval, after sending out of the paging signal, atstep 323 a paging signal 2 for the radio telephone handset at the nextorder of priority is sent out. At step 324, when the radio telephonehandset 5' receives the paging signal 2, at step 325, the transmitter 8'is turned ON to send out the paging response signal 2 at step 326. Whenthis paging response signal 2 is received by the base unit 4 within apredetermined interval after sending out the paging signal 2, theprogram is transferred to step 309 at which the transmitter 16 is turnedOFF, and then the channel is switched to speech channel (S-CH₂), wherebythe transmitter 16 is turned ON again to send out a bell ringing signalat step 315.

After sending out the paging response signal 2, the radio telephonehandset 5' executes the same operations as the radio telephone handset 5with respect to a portion 24 of the flow chart bounded by dotted lines.More particularly, transmitter 8' is turned OFF first for switching thechannel to the speech channel (S-CH₂) and turning ON again thetransmitter 8'. When a bell ringing signal is received from the baseunit, a call tone is sent out. When the hook switch 7' is taken off-hookin response to the call tone, an off-hook signal is sent out and thenthe audio frequency circuit is turned ON.

At step 316, when the base unit receives an off-hook signal from radiotelephone handset 5', at step 317, the line relay is turned ON so as toconnect the radio telephone handset 5' to the wired telephone line viathe base unit.

When the time out is judged at step 327, that is when no paging responsesignal 2 is sent back from radio telephone handset in a predeterminedinterval even though a paging signal 2 has been sent out, the program istransferred to step 329, thus bringing the base unit to the waitingstate.

FIG. 4 shows another flow chart in a case where a ring signal isreceived by the base unit from a wired telephone line. As can be notedfrom this flow chart, radio telephone handsets 5 and 5' intermittentlyreceive signals at different periods and the base unit sends a pagingsignal containing only the common identifying code. When either one ofthe radio telephone handsets 5 and 5' (in the flow chart telephonehandset 5') respond to the paging signal, both radio telephone handsets5 and 5' are connected to the predetermined speech channel (S-CH₂) so asto cause the telephone handset 5' to generate a call tone and thetelephone handset 5' which went off-hook in response to the call tone isconnected to the wired telephone line, whereas the radio telephonehandset 5 is brought to the waiting state.

At step 401 when there is a ring signal or the wired line, at step 402,the base unit 4 turns ON transmitter 16 for transmitting a paging signalover the control channel (C-CH) at step 403. As above described, thepaging signal contains only the common identifying code.

In a condition when radio telephone handsets 5 and 5' do not receive anysignal, they intermittently receive the signal at a predetermined period(battery saving operation). More particularly, at step 404, radiotelephone handset 5 turns OFF receiver 19 and as the set time of thetimer 1 elapses it turns ON receiver 19 at step 405. On the other hand,at step 407 where there is no received signal and the set time of timer2 has elapsed at step 408, the receiver 19 is turned OFF again. In thesame manner, at step 409 radio telephone handset 5' turns OFF receiver19'; and as the set time of time 3 has elapsed at step 410, the receiver19' is turned ON. At step 412 where there is no signal received, and atstep 413 the set time of timer 4 has elapsed, the receiver 19' is turnedOFF again.

Suppose now that a paging signal transmitted from base unit 4 at step403 is received by radio telephone handset 5' and that the receipt ofthe signal is judged at step 412. In this case, the program istransferred to step 414 so as to make a judgement as to whether thereceived signal is a paging signal or not. When the signal is the pagingsignal, at step 415, transmitter 8' is turned ON for sending out apaging response signal at step 416 and for turning OFF the transmitter417 at step 417. When the paging response signal is received by the baseunit 4 at step 419 in a predetermined interval after sending out thepaging signal at step 403, the base unit 4 sends out a channeldesignating signal that designates a predetermined speech channel atstep 420. After that, at step 421, transmitter 16 is turned OFF. Whenthe radio telephone handset 5 receives the channel designating signal atstep 423 in a predetermined interval after sending out the pagingresponse signal at step 416, and when the received signal is judged asthe channel designating signal at step 422, the program is transferredto the flow chart shown by dotted line block 24. This flow chart is thesame as the flow chart in block 24 shown in FIG. 3.

At step 407, the channel designating signal transmitted from the baseunit 4 is judged by radio telephone handset 5 at step 407, and then theprogram is transferred to step 424. In this case, since the signal isnot the paging signal, after switching the channel to speech channel(S-CH₃) at step 425, and the telephone handset is brought the waitingstate at step 426.

At step 421, after turning OFF transmitter 16, the base unit switchesthe channel to the speech channel (S-CH₃) at step 427 and then theprogram is transferred to the flow chart shown by block 25. The flowchart shown by this block 25 is the flow chart shown by block 25 in FIG.3. In FIG. 4, two flow charts shown by each of blocks 26 and 27 are thesame, respectively.

FIG. 5 shows a flow chart where a ring signal is received from the wiredtelephone line. The flow chart shown in FIG. 5 is a flow chart after thebase unit 4 and the radio telephone handsets 5 and 5' are connected tothe same speech channel in the same manner as the flow chart shown inFIG. 4. At step 501, the base unit 4 judges as to whether there is aring signal from the wired telephone line. When it is judged that thereis a ring signal, at step 502, a bell not-ringing signal is sent out,whereas when it is judged that there is no ring signal, at step 503, abell ringing signal is sent out. Whether the bell ringing signal isreceived or not is judged by radio telephone handset 5, for example atstep 504.

At step 505, when it is judged that the received signal is the bellringing signal, a call tone signal is sent out at step 506, and the hookswitch 7 is hooked OFF at step 507 in response to the call tone. Thentransmitter 8 is turned ON at step 508 to send out an off-hook signal atstep 509 which is received by base unit 4 at step 510, whereby the baseunit 4 turns ON the line relay 23 at step 511. At step 509, aftersending out the off-hook signal, the radio telephone handset 5 turns ONthe audio frequency circuit at step 512, thus establishing a speechstate at step 513.

At step 505, when it is judged that the bell ringing signal is notreceived, and at step 507, when it is judged that the hook switch is ONat step 507, that is when it is judged that the hook switch is not OFF,the program is returned to step 504. At step 510, when it is judged thatan OFF hook signal is not yet received, the program is returned to step501. At step 504, when it is judged that no signal is received, theprogram is returned to step 514 to bring the state to the waiting state.More particularly, with the flow chart shown in FIG. 5, when there is aring signal through a wired telephone line, both radio telephonehandsets 5 and 5' generate a call tone signal so that the first radiotelephone handset establishes a speech state, while the other radiotelephone handset reverts to the waiting state because there is nosignal received. In this case, by using only the bell ringing signal,the circuit is reverts to the waiting state when the bell ringing signaldoes not arrive for a predetermined interval.

FIG. 6 is a flow chart useful to explain the intercom operation betweenthe radio telephone handsets of the radio telephone system according tothis invention. Suppose now that radio telephone handset is in a speechmode while the other radio telephone handset 5' is in the waiting state.In this state, when intercom switch 32 of the radio telephone handset 5is turned ON at step 601, the radio telephone handset 5 sends out anintercom signal by using a speech channel at step 602. At step 603, whenthe base unit 4 receives this intercom signal, at step 604, the baseunit 4 sends out the bell ringing signal through the speech channel. Atstep 605, when the radio telephone handset 5' receives the bell ringingsignal, the telephone handset 5' sends out the call tone signal and whenthis radio telephone handset goes off-hook in response to the call tonesignal at step 607 and the audio frequency circuit of receiver 19' isturned ON at step 608, so that the radio telephone handset 5' isreceiving signals. On the other hand, the radio telephone handset 5 canmake speech while the intercom switch 32 is ON. Under this state, whenthe intercom switch 32' of the telephone handset 5' is turned ON at step609, the transmitter 8' of the radio telephone handset 5' is turned ONat step 610, whereby radio telephone handset 5' can exchange speech.When the intercom switch 32 is turned OFF at step 611, the transmitter 8of the radio telephone handset 5 is turned OFF at step 612, thusenabling only reception. In such an intercom state, unidirectionalspeech between radio telephone handsets 5 and 5' becomes possible byusing intercom switches 32 and 32' as press-to-talk switches.

When a system shown in FIG. 5 is adopted by using the intercom signal asa transfer signal, transfer of signals from radio telephone handset 5 toradio telephone handset 5' becomes possible. When the transfer is madepossible as above described, a special ringing tone may be issued thatrepresenting the transfer of the signal. It is possible to provideprivate speech by providing a private speech button switch. By operatingthis switch, reception by a radio telephone handset other than the radiotelephone handset capable of effecting bidirectional speech.

What is claimed is:
 1. A method of controlling a radio telephone systemof a type wherein connections between a wired telephone line and aplurality of radio telephone handsets are controlled by a single baseunit connected to said wired telephone line, comprising the stepsof:establishing a speech radio channel among said plurality of radiotelephone handsets and said base unit; turning OFF a transmitter of oneof said radio telephone handsets when an intercom switch on said radiotelephone handset is turned OFF; and turning ON a transmitter of saidradio telephone handset when said intercom switch on said radiotelephone handset is turned ON; wherein the step of establishing aspeech radio channel comprises: detecting a ring signal on said wiredtelephone line; sending a paging signal on a first radio channelincluding a channel designating signal to said plurality of radiotelephone handsets from said base unit when said ring signal isdetected; sending a paging response signal to said base unit from aresponding one of said radio telephone handsets when said paging signalis received; switching a radio channel of said responding radiotelephone handset to a speech radio channel designated by said channeldesignating signal; and switching a radio channel of said base unit to aspeech radio channel designated by said channel designating signal, whensaid paging response signal is received by said base unit within apredetermined time interval after sending out said paging signal fromsaid base unit.
 2. The method of claim 1 wherein the step of sending apaging signal comprises:sequentially sending the paging signal to saidplurality of radio telephone handsets from said base unit according to apredetermined order of priority.
 3. The method of claim 1 wherein thestep of sending a paging signal comprises:sequentially sending out thepaging signal to said plurality of radio telephone handsets from saidbase unit according to an order of priority that is randomly set foreach detection of said paging signal.
 4. The method of claim 1 whereinthe step of sending a paging signal comprises:sequentially sending outthe paging signal to said plurality of radio telephone handsets fromsaid base unit according to a predetermined order of priority which isset according to a speech hysteresis of respective radio telephonehandsets.
 5. The method of claim 4 wherein said predetermined order ofpriority is set such that a last one of said radio telephone handsetsfor which a speech channel was previously established has the highestpriority.
 6. The method of claim 1 wherein the step of establishing aspeech radio channel comprises:sending a bell ringing signal to saidresponding one of said radio telephone handsets from said base unitafter said base unit has been switched to the speech radio channeldesignated by said channel designating signal; producing an audible calltone in said responding one of said radio telephone handsets in responseto said bell ringing signal; and sending an off-hook signal to said baseunit from said responding one of said radio telephone handsets when saidresponding one of said radio telephone handsets is taken off-hook,thereby interconnecting said wired telephone line and said respondingone of said radio telephone handsets.
 7. The method of claim 1 whereinthe step of establishing a speech radio channel comprises:sending a bellringing signal to said responding one of said radio telephone handsetsfrom said base unit when said ring signal is detected and sending abell-not-ringing signal when said ring signal is not detected after saidbase unit has been switched to said speech radio channel; producing anaudible call tone in said responding one of said radio telephonehandsets in reponse to said bell ringing signal; sending, in response tosaid call tone, an off-hook signal to said base unit from saidresponding one of said radio telephone handsets when said selected radiotelephone handset is taken off-hook; and resetting said radio telephonesystem to a waiting state when said responding one of said radiotelephone handsets does not receive either said bell ringing signal orsaid bell-not-ringing signal, so as to interconnect said wired telephoneline with said responding one of said radio telephone handsets.
 8. Amethod of controlling a radio telephone system of the type whereinconnections between a wired telephone line and a plurality of radiotelephone handsets are controlled by a single base unit connected tosaid wired telephone line, said base unit and each said radio telephonehandset having a radio transmitter and a radio receiver, said base unitconnected to said radio telephone handsets by a radio channel, saidmethod comprising the steps of:designating a first radio channel forsaid plurality of radio telephone handsets in response to a ring signalon said telephone line; establishing a speech radio channel among saidplurality of radio telephone handsets and said base unit; turning OFFthe transmitter of a respective one of said radio telephone handsetswhen an intercom switch on said radio telephone handset is OFF; andturning ON the transmitter of the respective one of said radio telephonehandsets when said intercom switch on said radio telephone handset isturned ON.
 9. A method of controlling a radio telephone system of thetype wherein connections between a wired telephone line and a pluralityof radio telephone handsets are controlled by a single base unitconnected to said wired telephone line, said base unit and each saidradio telephone handset having a radio transmitter and a radio receiver,said method comprising the steps of:designating a first radio channelfor said plurality of radio telephone handsets in response to a ringsignal on said telephone line; establishing a speech radio channel amongsaid plurality of radio telephone handsets and said base unit; turningOFF the transmitter of a respective one of said radio telephone handsetswhen an intercom switch on said radio telephone handset is OFF; andturning ON the transmitter of the respective one of said radio telephonehandsets when said intercom switch on said radio telephone handset isturned ON; wherein the step of establishing a speech radio channelincludes the substeps of: detecting a ring signal on said wiredtelephone line; sending a paging signal on said first radio channelincluding a channel designating signal to said plurality of radiotelephone handsets from said base unit when said ring signal isdetected; sending a paging response signal to said base unit from aresponding one of said radio telephone handsets when said paging signalis received; switching a radio channel of said responding one of saidradio telephone handsets to a speech radio channel designated by saidchannel designating signal; and switching a radio channel of said baseunit to a speech radio channel designated by said channel designatingsignal, when said paging response signal is received by said base unitwithin a predetermined time interval after sending out said pagingsignal from said base unit.
 10. The method of claim 9 wherein the stepof sending a paging signal comprises:sequentially sending the pagingsignal to said plurality of radio telephone handsets from said base unitaccording to a predetermined order of priority.
 11. The method of claim9 wherein the step of sending a paging signal comprises:sequentiallysending out the paging signal to said plurality of radio telephonehandsets from said base unit according to an order of priority that israndomly set for each detection of said paging signal.
 12. The method ofclaim 9 wherein the step of sending a paging signalcomprises:sequentially sending out the paging signal to said pluralityof radio telephone handsets from said base unit according to apredetermined order of priority which is set according to a speechhysteresis of respective radio telephone handsets.
 13. The method ofclaim 12 wherein said predetermined order of priority is set such that alast one of said radio telephone handsets for which a speech channel waspreviously established has the highest priority.
 14. The method of claim9 wherein the step of establishing a speech radio channelcomprises:sending a bell ringing signal to said responding one of saidradio telephone handsets from said base unit after said base unit hasbeen switched to the speech radio channel designated by said channeldesignating signal; producing an audible call tone in said respondingone of said radio telephone handsets in response to said bell ringingsignal; and sending an off-hook signal to said base unit from saidresponding one of said radio telephone handsets when said responding oneof said radio telephone handsets is taken off-hook, therebyinterconnecting said wired telephone line and said responding one ofsaid radio telephone handsets.
 15. The method of claim 9 wherein thestep of establishing a speech radio channel comprises:sending a bellringing signal to said responding one of said radio telephone handsetsfrom said base unit when said ring signal is detected and sending abell-not-ringing signal when said ring signal is not detected after saidbase unit has been switched to said speech radio channel; producing anaudible call tone in said responding one of said radio telephonehandsets in response to said bell ringing signal; sending, in responseto said call tone, an off-hook signal to said base unit from saidresponding one of said radio telephone handsets when said selected radiotelephone handset is taken off-hook; and resetting said radio telephonesystem to a waiting state when said responding one of said radiotelephone handsets does not receive either said bell ringing signal orsaid bell-not-ringing signal, so as to interconnect said wired telephoneline with said responding one of said radio telephone handsets.
 16. Amethod of controlling a radio telephone system of the type whereinconnections between a wired telephone line and a plurality of radiotelephone handsets are controlled by a single base unit connected tosaid wired telephone line, said base unit and each said radio telephonehandset having a radio transmitter and a radio receiver, said methodcomprising the steps of:designating a first radio channel for saidplurality of radio telephone handsets in response to a ring signal onsaid telephone line; detecting in said base unit a ring signal on saidwired telephone line; sending a paging signal to said plurality of radiotelephone handsets from said base unit when said ring signal isdetected; sending a paging response signal to said base unit from saidradio telephone handsets in response to said paging signal; sending achannel designating signal to said radio telephone handsets in responseto said paging response signal; switching a radio channel of said baseunit to a speech radio channel designated by said channel designatingsignal; switching, in response to said channel designating signal, aradio channel of said radio telephone handsets to a speech radio channelcorresponding to said channel designating signal; turning OFF thetransmitter of a respective one of said radio telephone handsets when anintercom switch on said radio telephone handset is OFF; and turning ONthe transmitter of the respective one of said radio telephone handsetswhen said intercom switch on said radio telephone handset is turned ON.17. The method of claim 16 wherein the step of sending a channeldesignating signal comprises:sending said channel designating signal tosaid radio telephone handsets so as to switch the radio channels of saidradio telephone handsets to a speech radio channel designated by saidchannel designating signal.
 18. The method of claim 16 further includingthe steps of:sending a bell ringing signal to said radio telephonehandsets from said base unit after the radio channel of said base unithas been switched to the speech radio channel designated by said channeldesignating signal; producing, in each of said radio telephone handsets,a call tone in response to said bell ringing signal; and sending anoff-hook signal to said base station from each of said radio telephonehandsets when each of said radio telephone handsets is taken off-hook inresponse to said call tone, this interconnecting said wired telephoneline with a first one of said radio telephone handsets to send out anoff-hook signal.
 19. A method of controlling a radio telephone system ofthe type wherein connections between a wired telephone line and aplurality of radio telephone handsets are controlled by a single baseunit connected to said wired telephone line, said base unit and eachsaid radio telephone handset having a radio transmitter and a radioreceiver, said method comprising the steps of:designating a first radiochannel for said plurality of radio telephone handsets in response to aring signal on said telephone line; sending a call originating signalfrom an originating one of said radio telephone handsets; sending, fromsaid base unit and in response to said originating signal, a channeldesignating signal to said originating radio telephone handset;switching a radio channel of said base unit to a speech radio channeldesignated by said channel designating signal; switching, in response tosaid channel designating signal, the radio channel of said originatingradio telephone handset to a speech radio channel designated by saidchannel designating signal; turning OFF the transmitter of a respectiveone of said radio telephone handsets when an intercom switch on saidradio telephone handset is OFF; and turning ON the transmitter of therespective one of said radio telephone handsets when said intercomswitch on said radio telephone handset is turned ON.
 20. The method ofclaim 19 wherein the step of sending a channel designating signalcomprises:sending said channel designating signal to said radiotelephone handsets, to switch the radio channels of said radio telephonehandsets to the speech radio channel designated by said channeldesignating signal.
 21. The method of claim 19 wherein the step ofsending a channel designating signal comprises:sending said channeldesignating signal to only said originating radio telephone handset fromsaid base unit; and switching only the radio channel of said originatingradio telephone handset to the speech radio channel designated by saidchannel designating signal.
 22. The method of claim 19 further includingthe steps of:sending, in response to said originating signal, a callsignal from said base unit to a selected one of said radio telephonehandsets other than said originating radio telephone handset; andsending, in response to said call signal, a call response signal to saidbase unit from said selected one of said radio telephone handsets. 23.The method of claim 22 wherein the step of sending a channel designatingsignal comprises:sending a channel designating signal to said selectedone of said radio telephone handsets after a call response signal fromsaid one of said radio telephone handsets has been confirmed in responseto said call signal.
 24. The method of claim 22 wherein the step ofsending a channel designating signal comprises:sending the channeldesignating signal at a predetermined interval after sending said callsignal when a call response signal sent from said selected one of saidradio telephone handsets has not been confirmed in response to said callsignal.
 25. A method of controlling a radio telephone system of the typewherein connections between a wired telephone line and a plurality ofradio telephone handsets are controlled by a single base unit connectedto said wired telephone line, said base unit and each said radiotelephone handset having a radio transmitter and a radio receiver, saidmethod comprising the steps of:designating a first radio channel forsaid plurality of radio telephone handsets in response to a ring signalon said telephone line; establishing a speech radio channel between saidradio telephone handsets and said base unit; turning OFF the transmitterof a respective one of said radio telephone handsets when an intercomswitch on said radio telephone handset is OFF; turning ON thetransmitter of the respective one of said radio telephone handsets whensaid intercom switch on said radio telephone handset is turned ON;sending an intercom signal to said base unit from one of said radiotelephone handsets in response to an ON operation of said intercomswitch; sending, in response to receipt of the intercom signal, a bellringing signal to an addressed one of said radio telephone handsets fromsaid base unit; generating, in said addressed radio telephone handset,an audible call tone in response to said bell ringing signal; andenabling said transmitter of said addressed radio telephone handset whensaid addressed radio telephone handset is taken off-hook in response tosaid call tone.